What We Can Learn From Oysters

Exogyra ponderosa Oyster Fossil (Cretaceous Period 65 to 100 million-years-ago)

A lesson we can learn from oysters is that even though they have no heart to feel and no brain to reason, many of their species build massive reef communities which provide protection for one another; and not only for their own kind, but for many other ocean organisms. Very fittingly, they’ve been referred to as the “unshellfish”.

Exogyra is a large extinct oyster species that lived in the soft sediment of ancient shallow marine waters. It possessed a thick shell with a distinct pattern of ribbing and pitting representing growth lines. Many of its kind thrived during the Upper Cretaceous Period around 65 to 100 million years ago. Their shells opened using a strong abductor muscle to expose a foot which pushed it along and a siphon to filter food and take in oxygen from the ocean water. The abductor muscle scars on the valves are observable in the photo below.

Oyster Exogyra Insides
Exogrya ponderosa Oyster Fossil Upper and Lower Valves

Oysters and Love

In Greek mythology, the Greek Goddess of Love “Aphrodite” was said to have sprang up out of the ocean on an oyster shell. The term “Aphrodisiac”, meaning to heighten love, has been related to oysters ever since.  Also, the charismatic Casanova was known to have eaten twelve oysters a day, believing it would  enrich his love life.

Oyster Exogyra Under
Exogyra ponderosa Oyster Fossil Underside with Upper and Lower Valves in Closed Position


Scientific Name: Exogyra, ponderosa

Common Name: Oyster

Phylum: Mollusk (Large group of marine and fresh water invertebrates having soft bodies enclosed in a shell.)

Class: Pelecypod or Bivalve (Means hinged shell)

Order: Ostreoida (Means true oyster with irregular shell and adductor muscle; pearl oysters are not true oysters.)

Family: Gryphaeidae (Includes honeycomb oyster or foam oyster characterized under magnification with distinct shell structure.)

Genus: Exogyra (Extinct group of large, shallow-marine oysters possessing thick shells with distinctive spiraled peaks and ribbing on upper valves; lower valves were smaller and flattened.)

Species: Ponderosa

The Exogyra in my collection is a beautiful specimen that is quite heavy from being fossilized into solid stone. In the two photos above of its underside, you can clearly see how the valves fit together and how the lower valve is much smaller and flatter than the convex upper valve.

Graphea, navia (from Triasic 210mya - Jurassic 150mya
Pycnodonte Oyster Fossil, Upper and Lower Valves (Cretaceous 135 Million-Years-Ago to Miocene 40mya)

Today, the small oyster fossils shown above and below are found in abundance within shell-banks along North American coast lines. In their lifetime, they likely washed ashore during storms and were deposited on the beaches. Eventually, layers of sand and sediment buried them deep down cutting off oxygen and millions of year later, silica and other minerals permeated the shells and they fossilized.

Texigryphaea  oyster fossil (Cretaceous) 135mya - (Miocene) 40mya
Texigryphaea Oyster Fossil (Cretaceous 135 Million-Years-Ago to Miocene 40 mya)

Oysters For Food

Oysters have been a part of the human diet since Greek and Roman times. Today, two-billion pounds are eaten every year around the world. Oysters are prepared in a variety of ways, but raw on the half-shell is the most nutritious. Besides being an excellent source of protein, oysters contain rich sources of B vitamins, and scarce minerals such as calcium, iron, zinc, selenium and magnesium.

Graphea navia Oyster Fossil (Upper Triassic 210 Million-Years-Ago to Upper Jurassic 150 mya)

Hand Crafted Oyster Jewelry

Only one in 10,000 oysters produce a pearl, so human intervention has found a way to culture them artificially, but it still takes about six years for the oyster to complete the process. Many artists also craft beautiful jewelry using the shells of various oysters.

Exogyra, Graphea and Texigryphaea Extinct Oyster Fossil Rendering Drawing

Disclaimer: Room for error as I am about 90% certain on the identities of the small oyster shells.

All rights reserved © Fossillady 2022


Amazing Ammonites

Ammonite Fossil (Douvilleiceras, mammilatum)

Douvilleiceras mammilatum was a marine cephalopod ammonite, which are ancestors of today’s chambered nautilus. It possessed well-defined growth patterns on its shell (sutures). Douvilleiceras‘ knobs and spines are thought to be an indicator of a hostile environment. It lived during the Cretaceous Period (145 to 66 mya) and was unearthed in Madagascar (Albin Formation).

Cretaceous Period Oceanic Environment (145-66 million years ago) Artist Rendition
fossils 127
Mortoniceras sp Ammonite Fossil

The above fossil is a broken off section from another ammonite’s shell belonging to the genus, Mortoniceras sp. It was found in Arkansas in a dried up riverbed within the limestone, Goodland Formation. The shell is characterized by deep keels and ribbing. It lived mainly during the Cretaceous Period (145 to 66 mya). As with all the ammonites, its fate was doomed side by side with the dinosaurs.

fossils 126
Mortoniceras Ammonite Fossil (Top View)
Multi-purpose Tentacles

The ammonites were ocean predators grabbing their victims with precision and crushing them with their long, powerful tentacles. These tentacles contributed to another important function. They contained special sensors which facilitated their ability to navigate and locate prey in the vastness of the ocean.

A Complete Sample of Mortoniceras sp from Texas, Fort Worth Formation, Tarrant County
Function of Inner Chambers

Ammonites moved in spurts using a kind of jet propulsion by siphoning the ocean water into inner chambers inside their shells and then pushing the water out powerfully through a tube structure called a siphuncle. These inner chambers held water and special gases which helped it descend deep down ocean depths or float upward to shallower depths by filling and releasing the gases and water in and out of the chambers.

Ammonites possessed large heads and are assumed to have been highly intelligent like their cousin octopuses, squids, cuttlefish, nautilus etc. Scientist debate whether ammonites contained ink sacs for defense.

Inner Chambers of Ammonite Fossil

See two gigantic ammonite fossils from another article I have written (scroll to the bottom of article).


Scientific Name: Mortoniceras

Common Name: Ammonite

Kingdom: Animalia

Phylum: Mollusk (large diverse group of invertebrates possessing a shell, i.e. clams, snails, oysters, etc.)

Order: Ammonitida (characterized by thick, ribbed patterned shells)

Class: Cephalopod (means prominent head and tentacles, i.e. octopuses, cuttlefish, squids, nautilus)

Family: Brancoceratidae

Genus: Mortoniceras (characterized by deep keels, tubercules (knobs) and ribbing)

Mortoniceras Ammonite Rendering Drawing

Manuiceras sp (Ammonite)

Ammonite Dufrenoy
Ammonite Fossil

Manuicera sp. lived in the ancient seas when dinosaurs were around. In general, the ammonite’s plethora peaked during the Cretaceous Period (145 to 66 million-years-ago). But according to the fossil records, their incredible long history began as early as 440 mya during the Silurian Period.

Manuicera sp ammonite was unearthed from a dried up riverbed in Arkansas, they have also been unearthed in Texas. Both of these U.S. states lie within the limestone, Goodland Formation where many other Cretaceous fossils have been discovered. Originally, I mistakenly identified the fossil as, Dufrenoy justinae, but that was when I was newer to the field with a less discerning eye and research skills. So there you go. 

A variety of ammonite forms, from Ernst Haeckel‘s 1904 Kunstformen der Natur (Art Forms of Nature)

The amazing illustration above shows how ammonites vary greatly in the ornamentation (surface relief) of their shells. Some may be smooth and relatively featureless, except for growth lines. In others, various patterns of spiral ridges and ribs or even spines are shown.

Ammonite fossils have a world wide distribution indicating the theory of continental drift and due to their abundance (estimated 10 thousand species) scientists use them as date markers for other fossils along the same rock layers.

Some varieties grew to gargantuan sizes, larger than semitruck tires. You can see this in a photo from another article I have written, (scroll to bottom).


Scientific Name: Manuiceras sp. Common Name: Ammonite

Kingdom: Animalia

Phylum: Mollusk (soft body of invertebrate animal encased in shell)

Class: Cephalopod (means prominent head and tentacles, i.e. octopus, squid, cuttlefish, nautilus)

Order: Ammonitida (characterized by thick ribbed and patterned shells)

Family: Acanthoceratidae (possibly)

Genus: Manuiceras

Manuiceras sp Ammonite Rendering Drawing